Multicarrier waveforms, such as orthogonal frequency division multiplexed (OFDM) waveforms, have amplitude and phase information modulated thereon. These waveforms are conventionally amplified for transmission using linear or near-linear power amplifiers to reduce distortion of this information. The inherently low efficiency of these linear and near-linear power amplifiers results in increased power consumption and/or increased heat generation. Furthermore, the significant peak-to-average power ratios (i.e., 10-15 dB) of some multicarrier waveforms may further reduce the average efficiency of linear or near-linear power amplifiers. Increased power consumption and increased heat generation are undesirable characteristics, particularly for portable, mobile and handheld wireless devices that rely on batteries. Non-linear power amplifiers are generally more efficient than linear and near-linear power amplifiers, however direct amplification of a multicarrier waveform by non-linear power amplifiers may distort the amplitude and phase information, making non-linear power amplifiers unsuitable for use in conventional OFDM transmitters.
Many conventional transmitters use analog circuitry, which is more sensitive to process, voltage and temperature (PVT) variations than digital circuitry. Analog circuitry also utilizes large inductors that may occupy a larger die area and are less compatible with some semiconductor processes, such as complementary metal-oxide semiconductor (CMOS) processes, than digital circuitry. Analog circuitry may also require greater voltages than digital circuitry making it less compatible with low-voltage semiconductor processes.
Thus, there are general needs for multicarrier transmitters that are more efficient, consume less power, and/or are less sensitive to PVT variations. There are also general needs for multicarrier transmitters that are compatible with low-voltage semiconductor processes.